Distillation is a method of purifying a liquid (such as water) or, conversely, producing a concentrate (such as concentrated orange juice). In distillation, feed liquid to be distilled is heated to the point of evaporation, and the resulting vapor (e.g., steam) is collected and condensed.
Some distillation systems include rotary heat exchangers. One type of rotary heat exchanger includes vertically stacked, horizontally oriented annular plates that are disposed in a housing and mounted for rotation about a central vertical axis. An example of this type of heat exchanger is described in U.S. Pat. No. 6,238,524, which is assigned to the assignee of the present application and incorporated by reference herein in its entirety. Another type of rotary heat exchanger includes a vertically folded, accordion-shaped plate that is disposed in a housing and mounted for rotation about a central vertical axis. An example of this type of heat exchanger is described in U.S. patent application Ser. No. 09/609,881, which is also assigned to the assignee of the present application and incorporated by reference herein in its entirety.
Two factors that are commonly considered during design of rotary heat exchangers are cross-contamination and venting. Cross-contamination refers to the situation that results when the liquid being evaporated (e.g., unpotable water) comes into contact with and contaminates the resulting distillate, and venting refers to the removal of air and other gases that do not condense during distillation (i.e., non-condensables). Some rotary heat exchangers present risks of cross-contamination that make them unsuitable for generating potable distilled water, while other rotary heat exchangers remove non-condensables via complex flow paths that complicate fabrication and can reduce distillation efficiency.